Well there are shapeways creators http://www.shapeways.com/creator/ and there are personal co-creators. When you create your own co-creator you specify up to 3 fields where buyers can specify what ever you wish them to specify. An example would be a ring where the buyer could specify the size of the ring.

I learned a long time ago the wisest thing I can do is be on my own side, be an advocate for myself and others like me. -Maya Angelou
michael@shapeways.com Community Advocate